React hooks 的奇怪行为:延迟数据更新 [英] Strange behavior of React hooks: delayed data update

问题描述

奇怪的行为:我希望第一个和第二个 console.log 显示不同的结果，但它们显示相同的结果，并且仅在下次单击时更改值.我应该如何编辑我的代码以使值不同?

function App() {const [count, setCount] = React.useState(false);const test = () =>{控制台日志(计数)；//错误的setCount(!count);控制台日志(计数)；//错误的};返回 (<div className="应用程序"><h1 onClick={test}>你好 StackOverflow</h1>

);}const rootElement = document.getElementById("root");ReactDOM.render(, rootElement);

<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script><div id="root"></div>

您可以在这里看到一个工作示例:https://codesandbox.io/s/wz9y5lqyzk

解决方案

状态更新是异步的，所以如果你使用 Hooks，你可以使用 useEffect 在更新后收到通知.

这是一个例子:

https://codesandbox.io/s/wxy342m6l

如果你正在使用 React 组件的 setState，你可以使用回调

this.setState((state) => ({count: !state.count}), () => console.log('Updated', this.state.count));

如果需要状态值，请记住使用回调来更新状态.

Strange behavior: I expect that the first and the second console.log display a different result, but they display the same result and the value is changed only on the next click. How should I edit my code so that the value will be different?

function App() {
  const [count, setCount] = React.useState(false);
  const test = () => {
    console.log(count); //false
    setCount(!count);
    console.log(count); //false
  };
  return (
    <div className="App">
      <h1 onClick={test}>Hello StackOverflow</h1>
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="root"></div>

You can see a working example here: https://codesandbox.io/s/wz9y5lqyzk

解决方案

The state update is asynchronous so if you are using Hooks you can use useEffect to be notified after an update.

Here is an example:

https://codesandbox.io/s/wxy342m6l

If you are using setState of a React component, you can use the callback

this.setState((state) => ({count: !state.count}), () => console.log('Updated', this.state.count));

Remember to use the callback to update state if you need a state value.

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